(1) Field of the Invention
The present invention relates to a display device and, in particular, to a liquid crystal display device having higher reliability in the connection of terminal portions.
(2) Related Art Statement
Liquid crystal display devices have a TFT substrate on which pixel electrodes and thin film transistors (TFT's) are formed in a matrix and a facing substrate where color filters are formed in locations corresponding to the pixel electrodes, and liquid crystal is sandwiched between the TFT substrate and the facing substrate. In addition, the transmittance of light is controlled by liquid crystal molecules for each pixel, so that images are formed.
The TFT substrate is provided with video signal lines which extend in the longitudinal direction and are aligned in the lateral direction, and scanning lines which extend in the lateral direction and are aligned in the longitudinal direction, so that pixels are formed in regions surrounded by video signal lines and scanning lines. The pixels are mainly formed of a pixel electrode and a thin film transistor (TFT), which is a switching element. Thus, many pixels formed in a matrix form a display region.
In the display region on the TFT substrate, first TFT's are formed, an inorganic passivation film is formed from SiN on top of this, and an organic passivation film is further formed on top of this. The organic passivation film works to flatten the surface on which pixel electrodes are formed. Then, ITO, which is a transparent conductive film, is formed for the pixel electrodes on the flattened film.
Terminal portions for supplying power, video signals, scanning signals and the like to the display region from the outside are formed outside the display region on the TFT substrate. The terminal portions are formed in a process similar to that for the display region. That is to say, video signal lines and scanning lines extend to terminal portions through the sealing portion for pasting the TFT substrate and the facing substrate together so as to form a base metal for the terminal portions. The base metal for the terminal portions has the same layered structure as the video signal lines and the scanning lines.
The base metal for the terminal portions is covered with the inorganic passivation film and the organic passivation film. The inorganic passivation film and the organic passivation film are insulators, and therefore, through holes are created in these films in accordance with photolithography, so that it is possible for the terminal portions to be electrically connected to the outside. The metal easily corrodes in the air, and therefore, ITO, which is a chemically stable transparent conductive film, is formed so as to cover the through holes. There is an insulating film between the terminal portions. The organic passivation film has a particularly great film thickness as compared to the other insulating films. Accordingly, there is great unevenness in the terminal portions and the vicinity thereof as viewed in a cross section.
IC chips, such as video signal drivers, scanning signal drivers and the like, are connected to the terminal portions. In some cases, the IC chips are connected directly to the TFT substrate in accordance with a COG (chip-on-glass) method, and in other cases, the IC chips are mounted on a flexible film, which is then connected to the TFT substrate in accordance with a TAB (tape-automated bonding) method. In these cases, connection defects are easily caused, at the time of connection in accordance with COG and TAB methods, when there is great unevenness in the terminal portions.
In terms of cases where IC chips are connected in accordance with a COG method, Patent Document 1 describes a technology for reducing the thickness of the organic film in the terminal portions so that there is less unevenness in the terminal portions, and thus increasing the reliability in the connection of the IC chips in accordance with a COG method. As for cases where IC chips are connected in accordance with a COG method, Patent Document 2 described a technology for making the taper angle of the through holes created in the organic film in the terminal portions smaller than the taper angle of the through holes created in the organic film in the display region, and thus increasing the reliability in the connection of the IC chips. Patent document 3 describes a technology for reducing the film thickness of the organic film in the terminal portions and at the same time making the surface of the organic film uneven in the terminal portions so that the reliability in the connection between the film and the terminal portions can be increased when IC chips are connected in accordance with a TAB method.
(Patent Document 1) Japanese Unexamined Patent Publication 2002-229058 (Corresponding U.S. Application US2002/0145694 A1)
(Patent Document 2) Japanese Unexamined Patent Publication 2005-234091 (Corresponding U.S. Application US2005/0179849 A1)
(Patent Document 3) Japanese Unexamined Patent Publication 2006-195075 (Corresponding U.S. Application US2006/0152663 A1)